Reader Noise Reduction Using Spin Hall Effects

ABSTRACT

A read head is disclosed wherein a Spin Hall Effect (SHE) layer is formed on a free layer (FL) in a sensor and between the FL and top shield (S 2 ). Preferably, the sensor has a seed layer, an AP 2  reference layer, antiferromagnetic coupling layer, AP 1  reference layer, and a tunnel barrier sequentially formed on a bottom shield (S 1 ). When the stripe heights of the FL and SHE layer are equal, a two terminal configuration is employed where a current flows between one side of the SHE layer to a center portion thereof and then to S 1 , or vice versa. As a result, a second spin torque is generated by the SHE layer on the FL that opposes a first spin torque from the AP 1  reference layer on the FL.

This is a divisional application of U.S. patent application Ser. No.18/070,809; filed Nov. 29, 2022, which is a divisional application ofU.S. Pat. No. 11,587,582, issued on Feb. 21, 2023, which is a divisionalapplication of U.S. Pat. No. 11,205,447, issued on Dec. 21, 2021, all ofwhich are herein incorporated by reference in their entirety, andassigned to a common assignee.

RELATED PATENT APPLICATIONS

This application is related to the following: U.S. Pat. Nos. 9,437,225;and 10,559,318; assigned to a common assignee, and herein incorporatedby reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a reader structure wherein a Spin HallEffect (SHE) layer comprised of a giant positive or negative Spin HallAngle (SHA) material is formed between a free layer (FL) in a sensor anda top shield (S2), and wherein the reader is configured in a twoterminal design where a read current is applied between a bottom shield(S1) and one end of the SHE layer, or in a three terminal design where acurrent is applied between S1 and S2 while a second current (I_(SHE)) isapplied across the SHE layer in a longitudinal direction and a portionof the current splits off and flows through the sensor to S1 so thatspin torque from the SHE layer opposes spin torque from a referencelayer on the FL thereby substantially reducing spin torque noise in theFL, and increasing the sensor signal-to-noise ratio (SNR) and improvingthe bit error rate (BER) in recording to enable smaller sensor sizes andgreater areal density capability (ADC).

BACKGROUND

The hard disk drive (HDD) industry requires the magnetoresistive (MR)sensor in a read head of a combined read-write head to have a smallersize for better ADC. For current tunneling MR (TMR) sensors thattypically have a sensor resistance of around 300-600 Ohms, a reductionof the tunnel barrier RA (product of the resistance and area) isnecessary to keep the same sensor resistance as the lateral sizedecreases. However, an undesirable consequence of lower tunnel barrierRA is spin torque induced magnetic noise in sensors.

Spin transfer torque (hereinafter referred to as spin torque) arisesfrom the spin dependent electron transport properties offerromagnetic-spacer-ferromagnetic multilayers. When current passesthrough a magnetic multilayer in a CPP (current perpendicular to plane)configuration, the first ferromagnetic layer (FM1) that is a referencelayer, for example, will generate spin polarized currents as theelectrons traverse FM1. When the spin polarized current is transmittedthrough a polarization preservation spacer such as a tunnel barrier, thespin angular moment of electrons incident on a second FM layer (FM2)interacts with magnetic moments of FM2 (i.e. free layer) near theinterface between FM2 and the non-magnetic spacer. Through thisinteraction, the electrons transfer a portion of their angular momentumto FM2. As a result, spin-polarized current can influence themagnetization direction of a FL, or induce its dynamics, if the currentdensity in a read current between bottom and top shields (S1 and S2) ina sensor is sufficiently high.

FIG. 1A is a schematic depicting a typical read head sensor in HDD froman ABS perspective. A seed layer 2, AP2 reference layer 3 a,antiferromagnetic coupling (AFC) layer 3 b, AP1 reference layer 3 c,non-magnetic spacer 4, free layer 5, and capping layer 6 aresequentially formed on S1 84 and form a sensor between S1 and S2 87. TheAP1 layer has magnetization 3 m in a transverse direction (orthogonal tothe ABS) that is stabilized through AFC coupling with the AP2 layer. Thefree layer (FL) has magnetization 5 m that is free to rotate in and outof the ABS, and is biased in a cross-track direction with a longitudinalfield 7 m from magnetic biasing layers 7 on each side of the FL. The AP2layer is usually coupled to an antiferromagnetic (AFM) layer (not shown)that may be behind the sensor stack shown in FIG. 1A to reduce S1-S2spacing. Read current j1 may be applied from S1 to S2 or in the reversedirection.

As shown in FIG. 1B from a top-down view, with a local magnetic field 90m 1 or 90 m 2 from a magnetic medium bit (not shown) out of or into theABS 30-30, respectively, FL magnetization 5 m, which is in alongitudinal direction in the absence of a local field, rotates towardthe ABS (5 m 1) or away from the ABS (5 m 2) under the influence of thelocal field. Accordingly, alignment between magnetization 5 m 1 and 3 mis closer to the parallel state (P) with lower resistance, and alignmentbetween magnetization 5 m 2 and 3 m is closer to the anti-parallel state(AP) with higher resistance. For simplicity, the AP1 layer has a smallcanting angle (not shown) toward the longitudinal (y-axis) directionthat is neglected. Spin torque noise in the sensor depends on thepolarity of the current applied between S1 and S2. When positive currentflows from S2 to S1, electrons with negative charge are spin polarizedby AP1 to the FL direction and interact with the FL through spin torque.As a result, spin torque attempts to stabilize the P state anddestabilize the AP state. Therefore, when the local field 90 m 2 is intothe ABS (upward x-axis direction) and results in FL magnetization 5 m 2,spin torque noise at power level A is observed. On the other hand, whencurrent flows from S1 to S2, spin torque destabilizes the P state andstabilizes the AP state thereby causing higher spin torque noise atpower level B when the local field 90 m 1 is out of the ABS 30-30(downward x-axis direction) and results in FL magnetization 5 m 1. Powerlevel A is typically higher than B since the magnitude of the spintorque per area of the FL is proportional to the voltage across the TMRbarrier (non-magnetic spacer 4). Under a fixed current density, the APstate has a higher resistance, and thus a higher voltage drop and ahigher spin torque noise is the result.

The magnitude of the spin torque per area of the FL is proportional tothe voltage across the TMR barrier, and is anti-proportional to the RAof the barrier layer. Thus, for a sensor width >30 nm, RA is typicallyabove 0.7 Ohm-μm² where spin torque noise is not considered an importantfactor and where current polarity does not make a significant differencein noise level. For sensor widths in the range of 25-30 nm, RA around0.6 Ohm-μm² is needed, and restricting the current polarity to only thepreferred direction as described previously can limit the noise level toan acceptable magnitude for power level A. However, when sensor widthsbelow 25 nm, and RA below 0.6 Ohm-μm² or even below 0.5 Ohm-μm² arerequired, then spin torque noise increases to a level that is animportant concern for SNR even under the preferred current polarity.Thus, a new reader design is necessary to reduce spin torque noise,especially for reader sensors having a width <25 nm and RA below 0.6Ohm-μm² that are critical features in advanced HDD products.

SUMMARY

One objective of the present disclosure is to provide a reader designwhere the spin torque noise between an AP1 layer and FL in a sensor iseffectively canceled to provide better SNR and enable higher ADC,especially for sensor widths <25 nm.

A second objective of the present disclosure is to provide variousembodiments of the reader design according to the first objective thatallow for smaller shield to shield spacing, or for greater simplicity inthe fabrication process.

A third objective of the present disclosure is to provide a process flowfor forming a sensor that satisfies the first two objectives.

According to a first embodiment of the present disclosure, theseobjectives are achieved by forming a SHE layer between a FL in a sensorand a top shield (S2) in the reader. The SHE layer may be made of apositive giant SHA material such as Pt or a negative giant SHA materialsuch as β-Ta, and has a front side at the ABS in some embodiments, or isrecessed behind a portion of S2 in other embodiments to reduce shield toshield spacing (RSS). In another embodiment, the SHE layer replaces afront portion of S2 to minimize RSS. Preferably, the SHE layer iscomprised of a so-called giant SHA material having an absolute value forSHA that is >0.05, and is separated from S2 by an insulation layer. Inone preferred embodiment, the sensor stack has a seed layer, a referencelayer with an AP2/AF coupling/AP1 configuration, tunnel barrier, FL, andSHE layer sequentially formed on the bottom shield (S1).

The reader may be configured as a three terminal device where a currenthaving a first current density is applied from one side of the SHE layerand exits an opposite side with a lower current density since a portionof the input current is split off and flows through the sensor to S1.When the current with the first current density j is injected into theSHE layer and the portion that is split off with current density j1flows to S1, and spin polarization from the AP1 layer to the FL is P0,and AP1 magnetization is aligned out of the ABS, then the spin currentat density (j1×P0) with spin direction out of the ABS is injected intothe FL that causes FL magnetic noise. To offset the aforementionednoise, the SHE layer produces spin current with spin torque on the FL.For a (+) SHA material and a j2 direction from left to right at the ABS,the spin torque from the SHE layer will cancel the aforementioned FLmagnetic noise when (j2×SHA)=(j1×P0) where SHA is the spin polarizationof the SHA material to the FL. If a (−) SHA material is used, then thej2 direction is from right to left when j1 is from the SHE layer to S1.Alternatively, when j1 is from S1 to the SHE layer, then the directionof j2 in each of the aforementioned SHE layers made of (+) and (−) SHAmaterial is reversed.

In embodiments where the stripe height (SH) of the SHE layer isproximate to that of the FL, then the current density for j1 and j2 issubstantially the same and the reader may be configured as a twoterminal device to simplify the circuit and processing steps. Inparticular, one end of the SHE layer used in the three terminal devicedescribed previously may be etched away, or remain in place but with noconnection to a lead. For example, with a (+) SHA material, a current isdirected from the left side of the SHE layer to a center portion andthen proceeds down through the sensor stack to S1, or the direction ofthe current may be reversed so that spin torque from the SHE layer andAP1 layer on the FL cancel one another. When a (−) SHA material isemployed, the current direction is from the right side of the SHE layerto the center portion and then down through the sensor stack to S1, orin the reverse direction.

A process flow is provided for fabricating a sensor where an AFM layeris formed behind a front portion of S1 to reduce RSS. The SHE layerpreferably has a full width between the sides thereof so that the SHElayer sides are coplanar with the sides of S1 and S2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a reader structure wherein a sensor stackis formed between two shields (S1 and S2), and biasing layers are placedon each side of the sensor stack to bias the FL magnetization.

FIG. 1B is a top-down view of the AP1 layer and FL magnetizations inFIG. 1A, and shows how a local field from a medium bit influences the FLmagnetization to move toward or away from the air bearing surface (ABS).

FIG. 2 is a perspective view of a head arm assembly of the presentdisclosure.

FIG. 3 is side view of a head stack assembly of the present disclosure.

FIG. 4 is a plan view of a magnetic recording apparatus of the presentdisclosure.

FIG. 5 is a down-track cross-sectional view of a combined read-writehead with leading and trailing loop pathways for magnetic flux return tothe main pole according to an embodiment of the present disclosure.

FIG. 6 is an oblique view of a conductor made of a SHA material whereelectrons with spin in the (−) x-axis direction are deflected to the (+)z-axis surface, and electrons with spin in the (+) x-axis direction aredeflected to the (−) z-axis surface.

FIG. 7A is an ABS view of a reader sensor according to an embodiment ofthe present disclosure where a current is applied in a cross-trackdirection across a SHE layer made of a (+) SHA material and a portion ofthe current splits off and flows through the sensor to S1 to reduce spintorque noise within the free layer that is below the SHE layer.

FIG. 7B is an ABS view of the reader sensor in FIG. 7A showing that thecurrent pathways may be reversed to minimize spin torque noise withinthe free layer.

FIG. 8A is an ABS view of a reader sensor according to an embodiment ofthe present disclosure where a current is applied in a cross-trackdirection across a SHE layer made of a (−) SHA material and a portion ofthe current splits off and flows through the sensor to S1 to reduce spintorque noise within the free layer that is below the SHE layer.

FIG. 8B is an ABS view of the reader sensor in FIG. 8A showing thatcurrent pathways may be reversed to minimize spin torque noise withinthe free layer.

FIG. 9 is an ABS view showing input and output current for a SHE layer,and where a portion of input current with current density j2 is splitout to the j1 pathway through the free layer and a j pathway to anopposite side of the SHE layer according to an embodiment of the presentdisclosure.

FIG. 10A and FIG. 10B are alternative embodiments to FIG. 7A and FIG.7B, respectively, where the reader sensor is modified to a two terminaldevice by flowing a current j from one side of the (+) SHE layer to S1or in the reverse direction when the other SHE layer side is removed ordisconnected from a lead.

FIG. 11A and FIG. 11B are alternative embodiments to FIG. 8A and FIG.8B, respectively, where the reader sensor is modified to a two terminaldevice by flowing a current from one side of the (−) SHE layer to S1 orin the reverse direction when the other SHE layer side is removed ordisconnected from a lead.

FIG. 12 is a down-track cross-sectional view of a reader sensoraccording to an embodiment of the present disclosure where a front sideof the SHE layer is at the ABS, and the SHE layer stripe height isgreater than the FL stripe height.

FIG. 13 is a down-track cross-sectional view of a reader sensoraccording to an embodiment of the present disclosure where the SHE layeris recessed behind a front portion of S2 in order to reduce readershield to shield spacing (RSS).

FIG. 14 is a down-track cross-sectional view of a reader sensoraccording to an embodiment of the present disclosure where a front sideof the SHE layer is at the ABS, and the SHE layer is formed in front ofS2 to reduce the RSS.

FIGS. 15-18 are down-track cross-sectional views showing a sequence ofsteps in forming a sensor wherein a seed layer, AP2 layer, AF couplinglayer, AP1 layer, tunnel barrier, and FL are sequentially formed on S1,and an AFM layer is formed behind a portion of S1 according to anembodiment of the present disclosure.

FIG. 19 is a top-down view showing a step of patterning the sensor stackof layers in a cross-track direction.

FIGS. 20-21 are views from the eventual ABS plane that show a sequenceof etching a sensor stack to form sensor sidewalls, and then formingbiasing layers on each side of the sensor according to an embodiment ofthe present disclosure.

FIG. 22 and FIG. 23 are a down-track cross-sectional view and a top-downview, respectively, showing a step of patterning the SHE layer in aheight direction.

FIG. 24 is a down-track cross-sectional view of the sensor structure inFIG. 22 after an insulation layer is deposited behind the patterned SHElayer.

FIG. 25 is a down-track cross-sectional view of a reader sensoraccording to an embodiment of the present disclosure where a front sideof the SHE layer is at the ABS, and the SHE layer stripe height isessentially equal to the FL stripe height.

DETAILED DESCRIPTION

The present disclosure is a reader comprised of a sensor and that is ina combined read-write head wherein a SHE layer is formed between a freelayer (FL) in the sensor and a top shield (S2) so that when a current isapplied across the SHE layer in a cross-track direction, and a portionor all of the current flows in a down-track direction through the sensorin a three terminal or two terminal configuration, respectively, spintorque from the SHE layer offsets spin torque from a reference layer onthe FL to substantially reduce magnetic noise in the FL thereby reducingthe sensor SNR and improving BER. In the drawings, the y-axis is in across-track direction, the z-axis is in a down-track direction, and thex-axis is in a direction orthogonal to the ABS and towards a back end ofthe writer structure. Thickness refers to a down-track distance, widthis a cross-track distance, and height is a distance orthogonal to theABS in the x-axis direction. A magnetization in a transverse directionis orthogonal to the ABS, while a longitudinal direction is thecross-track direction. A back end or backside refers to a side of alayer facing away from the ABS, and a front side is a side of a layerfacing the ABS or at the ABS.

Referring to FIG. 2 , a head gimbal assembly (HGA) 100 includes amagnetic recording head 1 comprised of a slider and a PMR writerstructure formed thereon, and a suspension 103 that elastically supportsthe magnetic recording head. The suspension has a plate spring-like loadbeam 222 formed with stainless steel, a flexure 104 provided at one endportion of the load beam, and a base plate 224 provided at the other endportion of the load beam. The slider portion of the magnetic recordinghead is joined to the flexure, which gives an appropriate degree offreedom to the magnetic recording head. A gimbal part (not shown) formaintaining a posture of the magnetic recording head at a steady levelis provided in a portion of the flexure to which the slider is mounted.

HGA 100 is mounted on an arm 230 formed in the head arm assembly 103.The arm moves the magnetic recording head 1 in the cross-track directiony of the magnetic recording medium 140. One end of the arm is mounted onbase plate 224. A coil 231 that is a portion of a voice coil motor ismounted on the other end of the arm. A bearing part 233 is provided inthe intermediate portion of arm 230. The arm is rotatably supportedusing a shaft 234 mounted to the bearing part 233. The arm 230 and thevoice coil motor that drives the arm configure an actuator.

Next, a side view of a head stack assembly (FIG. 3 ) and a plan view ofa magnetic recording apparatus (FIG. 4 ) wherein the magnetic recordinghead 1 is incorporated are depicted. The head stack assembly 250 is amember to which a first HGA 100-1 and second HGA 100-2 are mounted toarms 230-1, 230-2, respectively, on carriage 251. A HGA is mounted oneach arm at intervals so as to be aligned in the perpendicular direction(orthogonal to magnetic medium 140). The coil portion (231 in FIG. 2 )of the voice coil motor is mounted at the opposite side of each arm incarriage 251. The voice coil motor has a permanent magnet 263 arrangedat an opposite position across the coil 231.

With reference to FIG. 4 , the head stack assembly 250 is incorporatedin a magnetic recording apparatus 260. The magnetic recording apparatushas a plurality of magnetic media 140 mounted to spindle motor 261. Forevery magnetic recording medium, there are two magnetic recording headsarranged opposite one another across the magnetic recording medium. Thehead stack assembly and actuator except for the magnetic recording heads1 correspond to a positioning device, and support the magnetic recordingheads, and position the magnetic recording heads relative to themagnetic recording medium. The magnetic recording heads are moved in across-track of the magnetic recording medium by the actuator. Themagnetic recording head records information into the magnetic recordingmedia with a PMR writer element (not shown) and reproduces theinformation recorded in the magnetic recording media by amagnetoresistive (MR) sensor element (not shown).

Referring to FIG. 5 , magnetic recording head 1 comprises a combinedread-write head. The down-track cross-sectional view is taken along acenter plane (46-46 described later with respect to FIGS. 19-21 ) thatis formed orthogonal to the ABS 30-30, and that bisects the main polelayer 14. The read head (reader) is formed on a substrate 81 that may becomprised of AlTiC (alumina+TiC) with an overlying insulation layer 82that is made of a dielectric material such as alumina. The substrate istypically part of a slider formed in an array of sliders on a wafer.After the combined read head/write head is fabricated, the wafer issliced to form rows of sliders. Each row is typically lapped to affordan ABS before dicing to fabricate individual sliders that are used in amagnetic recording device. A bottom shield (S1) 84 is formed oninsulation layer 82.

A magnetoresistive (MR) element also known as MR sensor 86 is formed onbottom shield 84 at the ABS 30-30 and typically includes a plurality oflayers (not shown) including a tunnel barrier formed between a referencelayer and a free layer where the FL has a magnetization (not shown) thatrotates in the presence of a local magnetic field from a magnetic bit toa position that is substantially parallel or antiparallel to thereference layer magnetization as described previously with regard toFIG. 1B. Insulation layer 85 adjoins the backside of the MR sensor, andinsulation layer 83 contacts the backsides of the bottom shield and topshield (S2) 87. The top shield is formed on the MR sensor. An insulationlayer 88 and a top shield (S2B) layer 89 are sequentially formed on S2.Note that the S2B layer 89 may serve as a flux return path (RTP) in thewrite head portion of the combined read/write head. Thus, the portion ofthe combined read/write head structure formed below layer 89 in FIG. 5is typically considered as the read head (reader). In other embodiments(not shown), the read head may have a dual reader design with two MRsensors, or a multiple reader design with multiple MR sensors.

The present disclosure anticipates that various configurations of awrite head (writer) may be employed with the read head portion. Theexemplary embodiment shows magnetic flux 70 in main pole (MP) layer 14is generated with flowing a current (not shown) through bucking coil 80b and driving coil 80 d that are below and above the main pole layer,respectively, and are connected by interconnect 51. Magnetic flux 70exits the MP layer at MP pole tip 14 p at the ABS 30-30 and is used towrite a plurality of bits on magnetic medium 140. Magnetic flux 70 breturns to the MP through a trailing loop comprised of trailing shield17, write shield 18, PP3 shield 26, and top yoke 18 x. There is also aleading return loop for magnetic flux 70 a that includes leading shield11, leading shield connector (LSC) 33, S2 connector (S2C) 32, returnpath 89, and back gap connection (BGC) 62. The magnetic core may alsocomprise a bottom yoke 35 below the MP layer. Dielectric layers 10, 13,36-39, and 47-49 are employed as insulation layers around magnetic andelectrical components. A protection layer 27 covers the PP3 trailingshield and is made of an insulating material such as alumina. Above theprotection layer and recessed a certain distance u from the ABS 30-30 isan optional cover layer 29 that is preferably comprised of a lowcoefficient of thermal expansion (CTE) material such as SiC. Overcoatlayer 28 is the uppermost layer in the writer.

In related U.S. Pat. No. 10,559,318, we disclosed the use of a SHE layerin a write head between a MP trailing side and the trailing shield. Whena current (I_(SHE)) is conducted across the SHE layer during a writeprocess and synchronized with the write current, spin transfer torque isgenerated on both of the MP trailing side and trailing shield to providea boost in transition speed and transition sharpness, and improved BER.Now we have discovered that the spin torque generated by flowing acurrent through a SHE layer may be advantageously employed in reducingmagnetic noise within a FL in a reader sensor.

Spin Hall Effect (SHE) is a physics phenomenon discovered in the mid20^(th) century, and is described by M. Dyaknov et al. in Physics Lett.A, Vol. 35, 459 (1971). Similar to a regular Hall Effect whereconduction carriers with opposite charges are scattered to oppositedirections perpendicular to the current density due to a certainscattering mechanism, SHE causes electrons with opposite spins to bescattered to opposite directions perpendicular to the charge currentdensity as a result of strong spin-orbit coupling in the conductinglayer. As shown in FIG. 6 , electrons pass through a non-magneticconductor 8 with strong spin orbit interaction, and electrons e2 withspin in the negative x-axis direction are deflected to the +z-axissurface 8 s 2 while electrons e1 with spin in the positive x-axisdirection are deflected to the negative z-axis surface 8 s 1. SHE isquantified by the Spin Hall Angle (SHA) defined as the ratio of the spincurrent in the direction transverse to the charge current (z-axis inFIG. 6 ) to the charge current (y-axis direction in FIG. 6 ). For manyyears after SHE was discovered, the absolute value of SHA materialsevaluated was typically <0.01, and SHE layers had very limitedapplications in industry.

During the past 10 years, materials with substantially larger (giant)SHA have been found. B. Gu et al. in Phys. Rev. Lett. 105, 216401(2010), and L. Liu et al. in Phys. Rev. Lett. 106, 036601 (2011)provided examples of SHA ˜0.07 in a Pt layer, and as large as 0.12 in Aulayers with Pt doping. A large but negative SHA of around −0.12 wasfound in β-Ta, meaning that electrons in the β-Ta layer are spinscattered in the opposite directions compared to what is shown in FIG. 6.

Referring to FIG. 7A, an ABS view of the reader with MR sensor 86 inFIG. 5 is shown according to a first embodiment of the presentdisclosure where a single SHE layer 9 made of a positive giant SHAmaterial contacts a top surface 5 t of FL 5 in the sensor. The sensor isa stack of layers with sidewalls 5 s 1, and wherein seed layer 2, AP2layer 3 a, AF coupling layer 3 b, AP1 layer 3 c, non-magnetic layer 4,and FL 5 are sequentially formed on S1 84. The non-magnetic spacer is atunnel barrier layer in preferred embodiments, but also may be a metalspacer in other embodiments. The MR sensor also typically comprises oneor more additional layers including an AFM layer (not shown) behind thestack pictured in FIG. 7A, and described later. FL magnetization 5 m islongitudinally biased with magnetization 7 m in biasing layers 7 formedwithin an insulation layer 85 a that contacts each sidewall 5 s 1 of theMR sensor. An upper portion of insulation layer 85 a separates eachbiasing layer from SHE layer 9. Note that the SHE layer has a full widthsuch that each side 9 s 1, 9 s 2 is coplanar with a side 84 s of S1 anda side 87 s of S2 87. Insulation layer 85 b is formed on the SHE layerand electrically separates the SHE layer from S2. Insulation layers 85a, 85 b are bottom and top portions, respectively, of insulation layer85 shown in FIG. 5 .

The benefit of the SHE layer 9 is explained as follows. Conductionelectrons in the input current in the SHE layer (hereinafter referred toas I_(in)) that flows in a positive y-axis direction with currentdensity j2 in the input direction at side 9 s 1, and current density jin the output direction at side 9 s 2, and that carry spin downwardpropagate to FL top surface 5 t. This spin polarization 9 psubstantially offsets a similar spin polarization (not shown) that isgenerated when a portion of the input current j2 splits off and flowswith current density j1 through sensor 86 to S1 84 and conductionelectrons in j1 that carry spin upward from AP1 layer 3 c produce spintorque on FL 5. In particular, spin current density represented by theproduct (j1×P0) where P0 is the spin polarization from AP1 to the FL ispreferably proximate to the spin current density represented by theproduct (j2×SHA) where SHA is the spin polarization from the SHE layerto the FL. In the ideal case where (j1×P0)=(j2×SHA), or optionally, when(j1×P0) is proximate to (j2×SHA), then spin torque induced magneticnoise within the FL is minimized to essentially zero or reducedsubstantially and will enable smaller sensor widths w1 with a smaller RAproduct of <0.6 in the tunnel barrier 4 for optimum performance. Notethat when sensor sidewalls 5 s 1 are non-vertical, width w1 refers tothe FL width.

SHE layer thickness t is preferably less than 12 nm since the L. Liureference mentioned earlier indicates that a SHE assist (spin torqueapplied to an adjacent magnetic layer, i.e. FL 5 in the presentdisclosure) is reduced when the giant SHA material has a thickness >12nm. Preferably, the absolute value for SHA is >0.05, and more preferablyis greater than 0.10 to enable a lower j2 current density. In someembodiments, the SHA material is a heavy metal that is one of β-Ta, Hf,Pt, Ir, and W that may be embedded with Au, for example. In otherembodiments, a topological insulator (Tl) may serve as a SHA materialaccording to a report atphys.org/news/2017-11-significant-breakthrough-topological-insulator-based-devices.html.A TI may be one of Bi₂Sb₃, Bi₂Se₃, Bi₂Te₃, or Sb₂Te₃, and has an innerportion that is an insulator or a high resistance material while anouter portion comprising the surface thereof has a spin-polarized metalstate. Therefore, the TI has an internal magnetic field such as a spinorbit interaction. A pure spin current can be generated in a highlyefficient manner due to the strong spin orbit interaction and collapseof the rotational symmetry at the surface.

Seed layer 2 typically includes one or more metals such as Ta, Ti, Ru,and Mg, an alloy such as NiCr, or a nitride (TiN or TaN) that promoteuniform thickness and the desired crystal growth in overlying MR sensorlayers. Each of AP2 layer 3 a, AP1 layer 3 c, and FL 5 may be a singlelayer or multilayer comprised of one or both of Co and Fe that may bealloyed with one or more of Ni, B, and with one or more non-magneticelements such as W, Mo, Ta, and Cr. AF coupling layer 3 b is typicallyone of Ru, Rh, Ir, or Os and has a thickness that ensures AP2 layer 3 ais AF coupled to AP1 layer 3 c. A non-magnetic spacer 4 that is a tunnelbarrier layer is preferably MgO but may be another metal oxide, metaloxynitride, or metal nitride used in the art. In other embodiments, thenon-magnetic spacer is a metal such as Cu. Insulation layers 85 a, 85 bmay be one or more of Al₂O₃, TaOx, SiN, AlN, SiO₂, MgO, and NiO. S1 84and S2 87 typically extend from a front side at the ABS to a backside(not shown) that is 10 microns or more from the ABS, have amagnetization saturation (Ms) value from 5 kiloGauss (kG) to 15 kG, andare generally comprised of CoFe, CoFeNi, CoFeN, or NiFe, or acombination thereof. In some embodiments, each biasing layer 7 is ajunction shield that is comprised of one or more magnetic materials suchas CoFe and NiFe. However, the biasing layer may also be a hard magneticmaterial that is CoCrPt or CoCrPtX where X is B, O or other elementsthat can assist a perpendicular growth of the HB easy axis, TbFeCo, or amultilayer ferromagnetic/non-magnetic super-lattice structure that is[Co/Pt/Co]_(n) or [Co/Pd/Co]_(n), for example, where n is a laminationnumber.

As shown in FIG. 7B, the first embodiment also encompasses a MR sensorhaving the three terminal configuration shown in FIG. 7A except where j1flows from S1 84 through sensor 86 to SHE layer 9, and merges with jthat flows in the negative y-axis direction from the right side 9 s 2 ofSHE layer 9 to give current density j2 in the output direction at theleft side 9 s 1. In this case, SHE layer spin polarization 9 p is in theopposite direction shown in FIG. 7A but still opposes spin polarization(not shown) from AP1 layer 3 c on FL 5 because j1 is also reversedcompared with the FIG. 7A configuration. As a result, the sameadvantageous result of reduced spin torque induced magnetic noise in theFL that enables a reduced SNR, lower tunnel barrier RA, and improvedreader performance for a MR sensor width w1<25 nm, is realized as inFIG. 7A when the product (j1×P0) is proximate or equal to the product(j2×SHA).

Referring to FIG. 8A, all aspects of the embodiment in FIG. 7A areretained except the (+) SHE layer is replaced with a negative giant SHAmaterial to give (−) SHE layer 9 n. Therefore, j2 in SHE layer 9 n isreversed compared with FIG. 7A and flows in the input direction fromside 9 s 2 and splits into j1 that flows through sensor 86 to S1 84 andj in the output direction to side 9 s 1 in order to achieve the sameeffect where spin torque produced by spin polarization 9 p from j2essentially cancels spin torque caused by spin polarization (not shown)from AP1 layer 3 c that is generated on FL 5. In other words, spintorque induced magnetic noise in the FL is effectively reduced to zero,or substantially decreased, to provide the same benefit mentionedpreviously for the FIG. 7A configuration when (j1×P0) is proximate orequal to (j2×SHA).

FIG. 8B depicts an alternative configuration for the embodiment in FIG.8A where all aspects are retained except the direction is reversed forj, j1, and j2. Thus, j1 flows from S1 84 through sensor 86 to SHE layer9 n, and merges with j that flows from side 9 s 1 to yield j2 that flowsto side 9 s 2 in SHE layer 9 n. Then the spin torque from the SHE layeressentially cancels the spin torque from AP1 layer 3 c when (j1×P0)equals or is proximate to (j2×SHA) as explained earlier.

In a conventional reader with an RA of 0.5 Ohm-μm², a voltage of about140 mV is generally applied across tunnel barrier 4. Thus, the resultingcurrent density is j1=2.8×10⁷ Amps/cm². Assuming the stripe height (SH2in FIG. 12 ) is substantially larger than the FL stripe height (SH1 inFIG. 12 ), the amount of current that is input from SHE layer side 9 s 1in FIG. 7A, for example, and split into the MR sensor current isnegligible. Thus, the injected current density j2 from side 9 s 1 andoutput current density j at side 9 s 2 in FIG. 7A are equal. Spinpolarization P0 from AP1 layer 3 c to FL 5 is typically 0.4-0.6, and theSHA for a giant SHE layer 9 is in the range of 0.1-0.2. Accordingly, j2should be a factor of 3-4 times j1 to satisfy the objective of(j1×P0)=(j2×SHA). It follows that the desired j2 of around 8-10×10⁷Amps/cm² is applicable in a SHE layer with good reliability. It shouldbe understood that in embodiments where (j1×P0) is proximate to(j2×SHA), a significant decrease in spin torque induced magnetic noisewithin the FL is still achieved compared with the prior art where thereis no SHE layer.

Referring to FIG. 9 , an enlarged view of SHE layer 9 and FL 5 from FIG.7A according to an alternative embodiment is depicted. If the stripeheight of the SHE layer 9 is equal to that of the FL 5, the currentI_(S) split from j2 into the FL and sensor cannot be neglected. Assumingthe FL has a width× SH1 of 24×24 nm² area for the j1 path, the SHE layerhas a thickness× SH2 of 6×24 nm² for the j2 path, the current densityfrom the left lead 94 into SHE layer side 9 s 1 is j_(in) and thecurrent density from side 9 s 2 to the right lead 95 is j_(out), thentotal input current I_(in) to the SHE layer equals the sum of outputcurrent split into the sensor (I_(S)) and the output current (I_(out))into the right lead where I_(out)×j_(in)=j_(out)+4 xj 1 because j1 has across-sectional area in the (x, y) plane that is a factor of 4 higherthan the cross-sectional area for j2 in the (x, z) plane, andj2=(j_(in)+j_(out))/2=j_(in)+2 xj 1, which is still in the applicableregime. Note that I_(in)=1.25×I_(S) and I_(out)=0.25× I_(S). The sameresult is realized for the alternative embodiments in FIG. 7B, FIG. 8A,and FIG. 8B where SH1 is essentially equal to SH2 (FIG. 25 ).

In FIG. 10A, another embodiment of the present disclosure is illustratedand is a modification of the reader in the first embodiment where thethree terminal device becomes a two terminal device. In particular, fora SHE layer 9 made of a giant positive SHA material, and when the stripeheight of the SHE layer is proximate to that of the FL, current throughthe SHE layer is substantially the same as the current through the MRsensor. In other words, current with current density j2 may be inputfrom a first terminal (not shown) and through a lead to SHE layer side 9s 1, and continues through sensor 86 with current density j1 to S1 84that serves as a second terminal. A key feature is that a right portion9 e of the SHE layer between dashed line 9 x and right side 9 s 2 iseither not connected to an output lead as in the first embodiment, or isremoved by etching and replaced with an insulation layer (not shown). Inaddition to the spin torque induced magnetic noise reduction in the FLassociated with the three terminal embodiments described earlier, thisembodiment has an additional advantage of simplifying the circuit andprocess steps. Note that the thickness and stripe height of the SHElayer may be adjusted so that product (j1×P0) is proximate or equal toproduct (j2×SHA) so that spin polarization 9 p from the SHE layeropposes spin polarization (not shown) from AP1 layer 3 c on FL 5 withthe overall outcome of substantially reducing or essentiallyeliminating, respectively, spin torque induced magnetic noise in the FL.

As shown in FIG. 10B, the reader configuration in FIG. 10A alsoencompasses an embodiment where current with current density j1 flowsfrom S1 84 upward through sensor 86 and to the SHE layer 9, and thenexits with current density j2 through SHE layer side 9 s 1 to a lead(not shown). In this case, SHE layer spin polarization 9 p is in theopposite direction shown in FIG. 10A but still opposes spin polarizationfrom AP1 layer 3 c on FL 5 because the j1 pathway through the AP1 layeris also reversed compared with the FIG. 10A configuration. Therefore,the same advantageous result of reduced spin torque induced magneticnoise in the FL that enables a reduced SNR, lower tunnel barrier RA, andimproved reader performance for MR sensor width w1<25 nm, is realized.

Referring to FIG. 11A, all aspects of the embodiment in FIG. 10A areretained except the (+) SHE layer is replaced with a negative giant SHAmaterial to give SHE layer 9 n. Moreover, the left portion 9 e of theSHE layer between dashed line 9 x and side 9 s 1 is either not connectedto an output lead as in the three terminal embodiment, or is removedwith an etching process and replaced by an insulation layer (not shown).A key feature is that current with current density j2 in SHE layer 9 nis reversed compared with FIG. 10A and flows from side 9 s 2 to a centerportion of the SHE layer and then continues with current density j1 downthrough MR sensor 86 to S1 84 in order to achieve the same effect wherespin torque produced by spin polarization 9 p in the SHE layeressentially cancels spin torque caused by spin polarization from AP1layer 3 c that is generated on FL 5.

Alternatively in FIG. 11B, the reader configuration shown in FIG. 11A isretained except the current pathway is reversed so that current withcurrent density j1 proceeds from S1 84 up through sensor 86, and thenexits SHE layer 9 n at side 9 s 2 with current density j2. Spinpolarization 9 p is in the opposite direction compared with the FIG. 11Aembodiment, but spin torque from the SHE layer continues to oppose spintorque from AP1 layer 3 c on FL 5 because the current pathway throughthe AP1 layer is also reversed.

In the two terminal device embodiments, an upper portion of FL 5proximate to top surface 5 t or an upper layer in a multilayer stack forthe FL preferably has a higher resistivity than the lower portion of theFL, and preferably a resistivity that is at least ˜5×10⁻⁷ Ohm·m. If theresistivity in the upper portion of the FL is too low, then the spintorque generated by SHE layer 9 (or 9 n) will be concentrated in the FLcorner nearer to the spin current injection side, which is side 9 s 1 inFIG. 10A and side 9 s 2 in FIG. 11A, or in the FL corner nearer the spincurrent exit, which is side 9 s 1 in FIG. 10B and side 9 s 2 in FIG.11B. Magnetic materials with B doping such as CoFeB, CoB, and FeBtypically have higher resistivity than non-B containing materials, andare preferred for an upper portion of the FL proximate to the SHE layersince they also do not reduce the TMR ratio. In other embodiments, theupper FL portion may contain a high damping impurity that is one of Re,Tb, or the like that also provides higher resistivity as long as theimpurity element does not diffuse into the tunnel barrier 4 and cause areduction in the tunneling magnetoresistive (TMR) ratio.

As indicated earlier, the present disclosure anticipates that the MRsensor in any of the previously described reader configurations may havedifferent locations for an AFM layer that is used to pin the AP2 layer 3a and thus stabilize the direction of magnetization 3 m in AP1 layer 3c. In conventional reader designs where reader shield to shield spacing(RSS) at the ABS is not a critical concern, then an AFM layer (notshown) may be formed between the seed layer 2 and AP2 layer 3 a in FIG.1A, for example. However, in more recent designs where reducing RSS isan important requirement, then the AFM layer may be recessed behind oneor more other layers in the MR sensor. In related U.S. Pat. No.9,437,225, we disclosed a MR sensor structure where an AFM layer isformed behind the FL, and in related U.S. Pat. No. 9,799,357, wedisclosed a MR sensor wherein the AFM layer is behind an upper portionof S1 in order to reduce RSS and pin related noise.

The present disclosure also encompasses reader designs with differentstripe heights and positions for SHE layer 9 (or 9 n). In the exemplaryembodiment shown in FIG. 12 that is a down-track cross-sectional view ofthe reader structure in one of FIGS. 7A-8B or in one of FIGS. 10A-11B,the SHE layer has a front side 9 f at the ABS 30-30, and a backside 9 bat a stripe height SH2. FL 5 has stripe height SH1 between the ABS andbackside 5 e, and magnetization 5 m in the absence of an external field.AP1 layer magnetization 3 m is AF coupled to AP2 layer magnetization 3 m1. The AFM layer that is typically employed to pin magnetization 3 m 1is not pictured in this drawing since the MR sensor may accommodatevarious AFM layer positions such as in U.S. Pat. No. 9,799,357, forexample. As explained previously, SH2 may be greater than SH1 in areader with a three terminal device configuration in FIGS. 7A-8B. Inother embodiments (FIGS. 10A-11B) where SH1 is proximate to SH2, thereader may have a two terminal device configuration where current withcurrent density j2 flows from one side of the SHE layer in alongitudinal direction to a center portion thereof, and then withcurrent density j1 in a down-track direction to S1, or in the reversepathway mentioned previously.

Referring to FIG. 13 , an alternative embodiment for the placement ofSHE layer 9 is depicted. A key feature is that front side 9 f isrecessed behind a portion of S2 front side 87 f to reduce RSS. The SHElayer has stripe height SH2, but a backside thereof is at height h1 fromABS 30-30 where h1>SH2. Insulation layer 85 b continues to separate theSHE layer from S2 87.

In yet another embodiment shown in FIG. 14 , the SHE layer front side 9f may be maintained at ABS 30-30, but S2 87 has a lower portion with afront side 87 f 2 that is recessed behind SHE layer backside 9 b inorder to reduce RSS. Meanwhile, an S2 upper portion has front side 87 f1 at the ABS. Here, SHE layer stripe height SH2 is less than FL stripeheight SH1, and less than height h2 that is the recessed distance of S2front side 87 f 2 from the ABS. FL 5 has a front side 5 f at the ABS.

The present disclosure also encompasses a process sequence forfabricating a SHE layer 9 (or 9 n) on a top surface 5 t of FL 5according to an embodiment described herein. The particular fabricationsequence that is illustrated relates to a reader with a MR sensor designwith an ABS view in one of FIGS. 7A-8B, a down-track cross-sectionalview shown in FIG. 12 , and an AFM layer placement described in relatedU.S. Pat. No. 9,799,357. However, various combinations of a two terminalor three terminal device with one of multiple alternative AFM layerpositions, and one of the SHE layer positions from FIGS. 12-14 areanticipated by the present disclosure as appreciated by those skilled inthe art.

Referring to FIG. 15 , a down-track cross-sectional view is shown wherea S2 bottom portion 84 a with top surface 84 t is provided. AFM layer20, ferromagnetic (FM) layer 21, AF coupling layer 22, and FM layer 23are sequentially laid down on the bottom shield. Optionally, FM layer 21and the AF coupling layer 22 may be omitted so that the AFM layer pins amagnetization (not shown) in FM layer 23, which in turn isferromagnetically coupled to AP2 layer 3 a (shown in FIG. 17 ). Thus,the AFM layer is responsible for pinning a magnetization in the AP2layer through a stack comprised of layers 21/22/23, or through a singleFM layer 23.

A first photoresist layer 60 is coated on FM layer 23 and is patternedby a conventional photolithography method to form a front side 60 f thatfaces the eventual ABS, which is indicated here by plane 30-30.Thereafter, a reactive ion etch (RIE) or ion beam etch (IBE) isperformed to remove uncovered portions of underlying layers and stops ontop surface 84 t to leave an opening 70 between plane 30-30 and plane44-44 that includes front side 60 f.

Referring to FIG. 16 , S2 top portion 84 b also known as a bottom shieldrefill and the seed layer 2 are sequentially deposited on S2 top surface84 t to a level that fills essentially all of opening 70 thereby forminga seed layer top surface 2 t that is coplanar with top surface 23 t onFM layer 23. The bottom shield refill is an extension of bottom shield84 a so that the bottom and top S2 portions may be collectively referredto as S2 84. A chemical mechanical polish (CMP) process may be performedto form coplanar top surfaces 2 t and 23 t.

Referring to FIG. 17 , AP2 layer 3 a, AF coupling layer 3 b, AP1 layer 3c, tunnel barrier 4, and FL 5 are sequentially laid down on seed layer 2and FM layer 23. The aforementioned sensor layers may be deposited in anAnelva C-7100 thin film sputtering system or the like which typicallyincludes three physical vapor deposition (PVD) chambers each havingmultiple targets, an oxidation chamber, and a sputter etching chamber.Next, a second photoresist layer 61 is coated on FL 5 and is patternwiseexposed and developed with a photolithography process to generate aphotoresist mask that extends from plane 30-30 to a backside 61 b atstripe height SH1 from the eventual ABS. Opening 71 exposes a portion ofFL top surface 5 t. It should be understood that the ABS is not defineduntil a back end lapping process occurs after all layers in the readhead and overlying write head are formed in combined read/write headstructure. For the purpose of more clearly describing the process flowin this disclosure, the eventual ABS is illustrated as a reference plane30-30. Thus, all layers contacting plane 30-30 actually extend to theopposite side of the eventual ABS until the lapping process isperformed.

Referring to FIG. 18 , patterned photoresist layer 61 is used as an etchmask during a RIE or IBE step that removes portions of the FL 5, andtunnel barrier 4 that are not protected by the etch mask. The etchingprocess stops on a back portion of AP1 layer top surface 3 t behind FLbackside 5 e where a bottom end at tunnel barrier 4 may be a greaterdistance from plane 30-30 than a top end at top surface 5 t. Note thatthe FL backside may be essentially vertical in other embodimentsdepending on FL thickness and the etching conditions. Then, insulationlayer 85 a is deposited with a top surface 85 t thereon. A planarizationstep may be performed to form a top surface 85 t that is coplanar withFL top surface 5 t. Insulation layer 85 a is preferably one or more ofAl₂O₃, TaOx, SiN, AlN, SiO₂, MgO, and NiO although other dielectricmaterials known in the art may be employed.

With regard to FIG. 19 , a photoresist layer 63 is coated on FL 5 andinsulation layer 85 a with backside 85 e, and is patternwise exposed anddeveloped with a conventional photolithography process to form aphotoresist mask having width w1 between sides 63 s that extend from afront side 63 f at the plane 30-30 to backside 63 e. Portions of FL 5are exposed on either side of center plane 46-46 between a side 63 s anda far side of the MR sensor structure at FL side 5 s. Portions ofinsulation layer 85 a are exposed between each photoresist mask side 63s and a far side 85 s of the insulation layer, and behind FL backside 5e.

FIG. 20 depicts a view of the partially formed MR sensor structure fromplane 30-30 after exposed portions of the sensor stack between eachphotoresist mask side 63 s and FL side 5 s in FIG. 19 are removed by anIBE process thereby forming a MR sensor side 5 s 1 that extends from FLtop surface 5 t to S1 refill top surface 84 t 2 on each side of centerplane 46-46. An opening 72 is generated on each side of the MR sensor.Insulation layer 85 a has a composition that provides a slower etchingrate than the sensor stack of layers to prevent etching into AP1 layer 3c behind plane 44-44 in FIG. 19 .

Referring to FIG. 21 , the MR sensor structure in FIG. 20 is depictedafter a second portion of insulation layer 85 a and biasing layer 7 aredeposited on S1 top surface 84 t 2 and on sidewall 5 s 1 to fill theopening 72. A planarization process may be used to form top surface 511that is coplanar with insulation layer top surface 85 t. Thus, eachbiasing layer 7 extends from the plane 30-30 to a backside at plane44-44 (not shown).

In FIG. 22 , SHE layer 9 (or 9 n) is deposited on FL 5 and on insulationlayer 85 a. Then, another photoresist is coated on the SHE layer andpatterned with a conventional method to yield photoresist mask 64 thatextends a stripe height SH2 from plane 30-30 to a photoresist maskbackside 64 e.

As shown from a top-down view in FIG. 23 , unprotected portions of theSHE layer are removed with an IBE or RIE step behind photoresist maskbackside 64 e. The photoresist mask has outer sides 64 s. The etch stopson or within insulation layer 85 a and thereby forms SHE layer backside9 b.

Referring to FIG. 24 , after photoresist mask 64 is removed, insulationlayer 85 b with top surface 8511 is deposited on SHE layer top surface 9t and on insulation layer 85 a. Thereafter, another photoresistpatterning and etch sequence well known to those skilled in the art maybe performed to generate a backside on the MR sensor stack of layers atplane 45-45.

The present disclosure also encompasses an annealing step after alllayers in the MR sensor structure have been deposited. A first annealingprocess may be performed to set the magnetization direction of the AP1layer 3 c and AP2 layer 3 a by heating the patterned MR sensor to atemperature range of 200° C. to 350° C. while applying a magnetic fieldalong the x-axis direction. A second annealing process is typically usedto set the direction of magnetization 7 m in biasing layers 7. If thetemperature and/or applied field employed during the anneal of biasinglayers 7 is lower than during annealing of the sensor stack, the firstannealing process may be performed before the second annealing processto maintain the AP1 and AP2 magnetization directions established duringthe first annealing process.

While the present disclosure has been particularly shown and describedwith reference to, the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the spirit and scope of thisdisclosure.

We claim:
 1. A read head, comprising: (a) a bottom shield (S1) having afront side at an air bearing surface (ABS), and a top surface; (b) a topshield (S2) having a front side at the ABS, and a bottom surface; (c) amagnetoresistive (MR) sensor formed on S1 at the ABS, comprising: (1) afree layer (FL) with a magnetization in a first cross-track(longitudinal) direction, a front side at the ABS, and a backside at afirst stripe height (SH1) from the ABS; (2) an AP1 reference layer witha magnetization that is orthogonal to the ABS in a first transversedirection, and wherein the AP1 reference layer is antiferromagnetically(AF) coupled to an AP2 reference layer through an AF coupling layer, andproduces a first spin torque on the FL when a current (j) flows throughthe MR sensor in a down-track direction; and (3) a non-magnetic layerbetween the FL and AP1 reference layer; and (d) a Spin Hall Effect (SHE)layer comprised of a negative Spin Hall Angle (SHA) material that isformed on the FL and with a second stripe height (SH2) between a frontside and backside thereof, and wherein a top surface of the SHE layer isseparated from the S2 bottom surface by an insulation layer, and whereinthe SHE layer is configured to generate a second spin torque on the FLthat opposes the first spin torque when the current (j) flows between afirst side of the SHE layer and a center portion thereof in a directionopposite to the first cross-track direction, or the current (j) flowsfrom S1 through the MR sensor and to the center portion of the SHElayer, and then to the first side of the SHE layer in the firstcross-track direction, and thereby reduces spin torque induced magneticnoise in the FL.
 2. The read head of claim 1 wherein the SHE layer has adown-track thickness less than 12 nm.
 3. The read head of claim 1wherein the SHE layer has an absolute value for SHA that is >0.05. 4.The read head of claim 1 wherein the SHE layer front side is at the ABS.5. The read head of claim 7 wherein the SHE layer backside is formedbetween the ABS and a bottom portion of S2 that has a front side atheight h2 from the ABS where h2>SH2.
 6. The read head of claim 1 whereinthe SHE layer front side is recessed behind a bottom portion of S2. 7.The read head of claim 1 wherein the MR sensor is further comprised ofan antiferromagnetic (AFM) layer that is formed behind an upper portionof S1, and wherein the AFM layer pins a magnetization in the AP2reference layer.
 8. The read head of claim 1 wherein SH2 is essentiallyequivalent to SH1.
 9. The read head of claim 1 wherein the non-magneticlayer is a tunnel barrier layer.
 10. A head gimbal assembly (HGA),comprising: (a) the read head of claim 1; and (b) a suspension thatelastically supports the read head, wherein the suspension has a flexureto which the read head is joined, a load beam with one end connected tothe flexure, and a base plate connected to the other end of the loadbeam.
 11. A magnetic recording apparatus, comprising: (a) the HGA ofclaim 10; (b) a magnetic recording medium positioned opposite to aslider on which the read head is formed; (c) a spindle motor thatrotates and drives the magnetic recording medium; and (d) a device thatsupports the slider, and that positions the slider relative to themagnetic recording medium.
 12. A method of forming a read head,comprising: (a) depositing a magnetoresistive (MR) sensor stack oflayers comprised of an AP1 reference layer, a non-magnetic spacer, and afree layer (FL) that are sequentially formed above a bottom shield (S1)top surface; (b) forming a backside on the FL that is a first stripeheight (SH1) from a first plane and extends from a FL top surface to abottom end at a top surface of the AP1 reference layer; (c) depositing afirst insulation layer on the top surface of the AP1 reference layer andthat adjoins the FL backside; (d) forming a sidewall on each side of theMR sensor stack of layers and that extends from the FL top surface tothe S1 top surface; (e) forming a biasing layer adjacent to each MRsensor stack sidewall that longitudinally biases a FL magnetization in across-track direction; (f) forming a Spin Hall Effect (SHE) layer on theFL wherein the SHE layer has a second stripe height (SH2) between afront side and a backside thereof, and wherein the AP1 reference layergenerates a first spin torque on the FL when a first current flows in adown-track direction through the MR sensor stack of layers, and the SHElayer generates a second spin torque on the FL that opposes the firstspin torque when a second current flows in a cross-track directionbetween one side of the SHE layer and at least a center portion thereof;and (g) performing a lapping process such that the first plane becomesan air bearing surface (ABS).
 13. The method of claim 12 wherein the SHElayer is comprised of a positive giant SHA material, or a negative giantSHA material having an absolute value for SHA that is >0.05.
 14. Themethod of claim 12 further comprised of forming a second insulationlayer on the SHE layer and a top shield (S2) on the second insulationlayer before the lapping process.
 15. The method of claim 12 wherein theSHE layer front side is at the ABS.
 16. The method of claim 13 whereinthe SHE layer backside is formed between the ABS and a bottom portion ofS2 that has a front side at height h2 from the ABS where h2>SH2.
 17. Themethod of claim 14 wherein the SHE layer front side is recessed behind abottom portion of S2.
 18. The method of claim 12 wherein SH2>SH1, andthe first current that is in a down-track direction flows between S1 andS2, and the second current in a cross-track direction across the SHElayer flows from a first side of the SHE layer to a second side of theSHE layer.
 19. The method of claim 12 where SH2 is essentially equal toSH1, the first current is the second current, and the second current inthe cross-track direction flows from one side of the SHE layer to thecenter portion, and then in a down-track direction through the MR sensorstack of layers to S1, or the first current in the down-track directionflows from S1 through the MR sensor stack of layers to the centerportion of the SHE layer, and then in the cross-track direction to oneside of the SHE layer.
 20. The method of claim 12 wherein thenon-magnetic spacer is a tunnel barrier layer.
 21. The method of claim12 wherein the MR sensor stack of layers is further comprised of a seedlayer on S1, an AP2 reference layer on the seed layer, anantiferromagnetic (AF) coupling layer that antiferromagnetically couplesthe AP1 and AP2 reference layers, and an AFM layer formed behind anupper portion of S1 wherein the AFM layer pins a magnetization in theAP2 reference layer.